The present invention relates to an optical transmitter/receiver module for transmitting optical signals, and more particularly, to an optical printed circuit board system including an optical printed circuit board with tapered optical waveguides and having improved coupling efficiency of optical signals when connecting the tapered optical waveguides to one another.
2. Description of the Related Art
With the advance of integrated circuit technology, the speed and the degree of integration of integrated circuits have greatly improved. Accordingly, high-performance microprocessors and large capacity memory chips are becoming a reality very fast. In this regard, it is required to increase the speed of signal transmission and the volume of signals transmitted between devices or between system boards on which the devices are mounted and form a specified circuit.
Until now, electrical signals have been used to transmit data to a short distance, between boards within a system for signal transmission or between chips within a board. However, when, for example, next generation information technology systems including large capacity parallel computers and more than terabits level ATM switching systems are introduced, thereby increasing the need for a faster and a large volume of data transmission, the performance of circuit systems will have to be improved accordingly. In addition, the speed of signals and the density of signal wirings must be enhanced.
However, in electrical signal wirings, it is hard to further enhance the speed of signals and the intensity of signal wirings, which is aggravated by signal delays in wirings. In particular, electromagnetic interference (EMI) noise accompanies high-speed electrical signals and high-density electrical signal wirings. Hence, a solution to prevent the EMI noise is needed.
As a solution to these problems, PCB concepts using optical lines instead of electrical lines have been introduced. It is expected that optical lines can be applied to signal transmission between systems or between boards included in a system or between chips included in a board.
Conventional optical PCB related technologies are mostly based on a silicon substrate and focused on including a silicon chip for transmitting signals, an optical emitter, an optical substrate, an optical detector, and a silicon chip for receiving signals in the silicon substrate. The conventional optical PCB related technologies include a lens for optical coupling. To transmit optical signals, an optical line is mounted on the surface of an optical back plane, which is a kind of an optical PCB for signal connection between system boards. However, the optical PCB configured in this way is just a modification of an optical transmitter/receiver module and a little different, in terms of technical characteristics.
A representative optical PCB technology is disclosed in U.S. Pat. No. 6,324,328 patented on Nov. 27, 2001. The optical PCB technology in this patent suggests a PCB including an optical waveguide as an optical wiring for signal transmission. However, this optical PCB technology fails to remove an obstacle to realizing optical PCBs, that is, an alignment between optical signals when transmitting optical signals.
NTT Corporation of Japan suggests a prototype using an existing SMT system. In the prototype, a surface-emitting laser and a photodiode are adhered to a hole in the rear of a plastic BGA package, and two polymer micro-lenses are positioned on one optical path, thereby increasing an allowable mounting margin.
The prototype enables optical signals to be transmitted in parallel between IC packages and substantially reduces a cost of mounting. However, the prototype may still have three misalignment problems. In other words, a first misalignment may occur when accumulating optical waveguides in a PCB. A second misalignment may occur when adhering a surface-emitting laser to the rear of a plastic BGA package. Finally, a third misalignment may occur when soldering the plastic BGA to the PCB, which is a second wiring interconnection. Moreover, the surface-emitting laser has a completely closed structure and fails to present ways to spread or cool off heat generated by chips.
To increase the use of optical PCBs or to smoothly release the optical PCBs in the market, a higher production cost of the optical PCBs than that of conventional PCBs and the problem of aligning optical lines must be tackled before everything else. A high production cost is mainly caused by a complicated manufacturing process designed to overcome the misalignment problem. For example, a silicon optical bench adopted for exact alignment accounts for more than 30 percent of the optical PCB production cost. Various ways to solve the problem of arranging optical lines are being tried but optical coupling efficiency remains still low. Therefore, intensive studies are being conducted to seek ways to enhance optical coupling efficiency and provide an optical PCB having a more economical and effective optical connection.